This invention relates to pumps, and more particularly it deals with a vane pump.
Generally, a vane pump comprises a housing including a cylindrical pump chamber, a cylindrical drive rotor arranged eccentrically in the pump chamber and adapted to rotate such that it is disposed in close proximity to a portion of the inner wall surface of the pump chamber, and a plurality of vanes rotatably supported by a vane shaft arranged in the center axis of the pump chamber. The vane shaft is mounted to be disposed within the drive rotor while each vane extends outwardly of the drive rotor through one of slits formed in the cylindrical portion of the drive rotor, so that its outer end is disposed in the neighborhood of the inner wall surface of the pump chamber. In the pump constructed as aforesaid, the drive rotor rotates to cause the vanes to rotate so that the pumping action may be performed. The efficiency of the pump is greatly influenced by the airtight sealing effect provided between the vanes and the drive rotor.
The vanes each extend outwardly through one of the slits formed in the cylindrical portion of the drive rotor. Portions in which airtight seal must be provided are between each slit and opposite surfaces of one of the vanes and between the end walls at the opposite side ends of the cylindrical portion of the drive rotor and the opposite end faces of each vane. A sealing material is generally mounted between each slit and opposite surfaces of one of the vanes. However, no sealing material is provided between the side end faces of each vane and the end walls of the drive rotor. By minimizing the clearance between them, these portions are substantially sealed.
Forces which are complicated act on the vanes and the vane shaft supporting the vanes during rotation of the vanes and the drive rotor. As a result, the vanes may move axially of the vane shaft and the side end faces of the vanes may be brought into collision with one of the end walls of the drive rotor. The vanes move in complicated swinging motion relative to the end walls of the drive rotor. Thus, if the side end faces of the vanes are in contact with one of the end walls of the drive rotor, the vanes and the drive rotor will move in sliding swinging motion relative to one another. This sliding swinging motion will cause wear to the respective sliding surfaces, so that the clearance between the end faces of the vanes and the end walls of the drive rotor will increase and the volume of fluid discharged by the pump will decrease.
This sliding swinging motion increases in magnitude as the number of revolutions of the vanes increase, with an attendant increase in the wear caused to the sliding surfaces. In a vane pump which is operated at high speeds as is usually the case nowadays, the sliding surfaces of the vanes and the drive rotor wear off quickly, so that the vane pump has a short service life. In case the vanes are fabricated by cutting a plate formed by connecting together glass fibers with a phenol resin as is usually done nowadays, the glass fibers tend to be broken at the cut and converted into particles which find their way between the sliding surfaces of the vanes and the drive rotor. This promotes wear of the sliding surfaces of the vanes and the drive rotor, thereby further reducing the durability of the pump.